% From The Art of Eyepl, Chapter 6.
next(X, Y) :- (Y is X + 1).
area_rectangle(W, H, Area) :- (Area is W * H).

hypotenuse(A, B, C) :-
  (A2 is A * A),
  (B2 is B * B),
  (C2 is A2 + B2),
  (C is sqrt(C2)).